Red ceramic and concrete waste as replacement of portland cement: Microstructure aspect of eco-mortar in external sulfate attack

Abstract

The use of red ceramic and concrete waste as a replacement for cement has great importance from an environmental point of view, and it is necessary to understand its influence on the cement matrix's performance. In this paper, mortar mixtures with partial replacement of the Portland cement by the addition of 3, 5, 12, and 20% of limestone filler (as reference), concrete waste, and red ceramic were subjected to sulfate attack. The accelerated test was monitored until the age of 98 days and microstructure analysis techniques were applied. Mortars with ceramic and concrete waste addition had greater expansion than the reference mortar. The addition of 12% of limestone filler mitigated the expansive reactions. The mortars with any type of addition had greater porosities. In this case, the aluminum oxide content in the ceramic and the calcium carbonate and calcium oxide contents in the concrete waste acted as a source for reaction with the sulfate ions. Due to the attack, the pore size distribution changed, showing that the pores in the band between 0.01 and 1 µm were filled with ettringite. The microcracks from the attack increased the pores with diameters over 1 µm. This performance reduction against sulfate attack must be considered for the use of ceramic and concrete residues in eco-efficient mortars, especially when it is inserted in environments subjected to this type of degradation.